Differential current circuit breaker and a method of setting the tripping ranges

• US 5,195,008 A
• Filed: 04/23/1990
• Issued: 03/16/1993
• Est. Priority Date: 04/24/1989
• Status: Expired due to Fees

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Harr, Dieter
• Primary Examiner(s): DEBOER, TODD
• Application Number:
  US07/512,964
• Time in Patent Office: 1,058 Days
• Field of Search: 361/42-45, 361/93, 361/94, 361/58
• US Class Current: 361/42
• CPC Class Codes: H02H 3/332 with means responsive to dc component in the fault current

Abstract

A differential current circuit breaker is disclosed in operation with a transductor circuit. The transformer has a secondary winding which is coupled to a measuring resistor in series with a generator, in particular a square wave generator, for alternating magnetization. The circuit breaker includes an evaluation circuit coupled to a tripping mechanism that acts through a breaker mechanism on switching contacts in the conductors being monitored. The evaluation circuit is coupled to a tap between the secondary winding and the measuring impedance. The generator capable of setting the generator frequency within a larger frequency range than is required to compensate for tolerance adjustment in the generator itself.

Claims

1. A differential current circuit breaker operating with a transductor circuit monitoring a plurality of conductors, comprising:

a transformer having a primary winding in series with all of said plurality of conductors to be monitored and a secondary winding;

a measuring impedance in series with said secondary winding;

a voltage generator providing an alternating output signal, wherein a frequency of said alternating output signal is adjustable over a frequency range larger than a frequency range required to compensate for tolerance in said voltage generator, said voltage generator coupled to and supplying said output signal through said secondary winding and said measuring impedance;

an evaluation circuit having an input coupled to a tap located between said secondary winding and said measuring impedance;

a tripping mechanism responsive to said evaluation circuit;

switching contacts in said conductors to be monitored; and

a breaker mechanism coupled to open and close said contacts of said breaker mechanism responsive to said tripping mechanism to open said contacts.

2. The differential current circuit breaker of claim 1, wherein said generator is a square wave generator.

3. A method of setting the tripping range of a circuit breaker which includes:

a transformer having a primary winding in series with a plurality of conductors to be monitored and a secondary winding;

a measuring impedance in series with said secondary winding;

a voltage generator providing an alternating output signal, wherein a frequency of said alternating output signal is adjustable over a frequency range larger than a frequency range required to compensate for tolerance in said voltage generator, said voltage generator coupled to and supplying said output signal through said secondary winding and said measuring impedance;

an evaluation circuit having an input coupled to a tap located between said secondary winding and said measuring impedance;

a tripping mechanism responsive to said evaluation circuit;

switching contacts in said conductors to be monitored; and

a breaker mechanism coupled to open and close said contacts of said breaker mechanism responsive to said tripping mechanism to open said contacts

said method comprising;

(a) supplying to said breaker a sample series of current at which tripping is required;

(b) setting the frequency of said generator to cause said breaker to trip.